Created attachment 278453 [details] [review]
Patch to fix selector for drag-and-drop of column headers

Custom-drawn widget that want to look like a TreeView often paint the
column header directly, so they apply the button class at the same level
than the column-header widget.

This is the case for example to the track list in Banshee (GTK 3 port in progress).

This means that selectors like "column-header .button..." do not match,
there needs to be the equivalent "column-header.button...". This is
already the case in a lot of places, but is missing for the "dnd"
class.

I'm attaching a one-line patch to correct this.